Mercer came into the season playing well but this is starting to look like who he is. A third line player who's a 50 pt player on a good team. If you can trick a GM into giving up something big with him as the main piece, sure, take it. I just don't think it works cap-wise right now. His deal is looking, at best, appropriate for who he is right now.
But if Barry was still infatuated and straight up would do Mercer for O'Reilly, I don't think I'd say no, even if ROR is on the downswing. At least you're getting someone with more of a pulse at that slot.
Haula, at least you can say he's in line with his career averages. This is who he is for the most part. Ditto for Cotter.
It would be nice for the 4th line to matter but I don't think it does. Mercer and Haula not generating enough is really the biggest issue.